Standard car tyres have a symmetrical tread pattern that is the same across the whole width of the tyre. The tread pattern on an asymmetric car tyre changes across the tread with different parts adapted for particular functions.
The outside edge consists of large stiffer tread blocks which help with cornering. The inner tread blocks are smaller and designed to shift water and improve wet grip. The middle of the tread usually has a continuous rib to help straight line stability.
Asymmetric tyres must be fitted the right way round on the wheel to benefit from the tread block arrangement. The sidewalls will be clearly marked.